1. Field
Aspects of the exemplary embodiments relate to a mass-airflow rate measurement for an internal combustion engine, and more particularly to a mass-airflow rate measurement conversion apparatus for internal combustion engine carburetors and a method of retrofitting existing internal combustion engine carburetors with a mass-airflow rate measurement conversion apparatus for internal combustion engine carburetors.
2. Description of the Related Art
Over the last 30 years, an increasing proportion of internal combustion engines have been equipped with electronic fuel injection (EFI). Among the reasons for the switch to EFI, increased reliability, performance, and longevity are key factors, along with significantly tighter engine calibration over the full engine operating range. As of the end of the 1990's, practically all original equipment passenger car engines were converted from carburetion to EFI, and smaller engines like those used on motorcycles quickly followed suit.
The automotive aftermarket also followed the trend, offering EFI conversion systems for existing engine applications. Many of these systems were offered as retrofits to existing carburetion-equipped motors, with the carburetor eliminated and replaced with a throttle body for air flow regulation. A majority of these EFI implementation utilized speed-density (SD) fueling calculation methods, which uses the intake manifold air pressure and temperature to determine cylinder air charge density. The requirement of a SD system is the determination of engine Volumetric Efficiency (VE) as part of the engine calibration process, which can be a difficult task to accomplish without dynamometer facilities and accurate Air-Fuel Ratio (AFR) determination.
Another method of mass air determination for EFI systems is with the use of an external Mass-Air Flow meter (MAF). The use of a MAF sensor is very practical in an aftermarket installation in that it significantly reduces the engine calibration effort.
A significant downside of employing an external MAF sensor in an aftermarket EFI conversion is the fitting and plumbing required to implement a MAF sensor. MAF sensors are very sensitive to upstream and downstream bends or other changes in physical geometry affecting the air stream. These changes in physical geometry can greatly alter the calibration of the MAF sensor's transfer function (i.e., mass air flow to voltage or frequency), thus increasing the installation effort. In addition, for some installations there is a desire to maintain the original “look” of a carburetor without the extra plumbing and duct work required for a proper MAF sensor installation.
Another downside to aftermarket MAF sensor installations is that of intake manifold “filling and emptying” effects. This effect is an artifact change in indicated mass air flow due to changes in throttle position which do not represent the actual engine mass air intake. This effect, if not compensated, can lead to fuel rich conditions during transitions to wide-open throttle and fuel lean situations for rapid throttle closings.